Led lamp

ABSTRACT

An LED lamp that can take the place of incandescent lamps. An elevated light source is positioned above a screw-type base. A first plurality of LEDs is connected in a series on one side of a flat substrate and a second plurality of LEDs, equal in number to the first, is connected in series on an opposite side of the substrate. Each LED of the first and second plurality of LEDs is mounted proximate a heat sink and a drive circuit is provided for the LEDs, with the drive circuit being located proximate and electrically connected to the screw base.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. application Ser.No. 15/370,723, filed Dec. 6, 2016, which application is a continuationof U.S. application Ser. No. 15/015,834, filed Feb. 4, 2016, whichapplication is a continuation of U.S. patent application Ser. No.14/638,406, filed Mar. 4, 2015 and now U.S. Pat. No. 9,267,649; whichapplication is a continuation of U.S. patent application Ser. No.13/855,391, filed Apr. 2, 2013 and now U.S. Pat. No. 9,016,901; whichapplication is a continuation of U.S. patent application Ser. No.12/826,774, filed Jun. 30, 2010 and now U.S. Pat. No. 8,408,748; whichapplication is a continuation-in-part of International Application No.PCT/US2009/030741, filed Jan. 12, 2009; which application claimspriority from U.S. Provisional Application No. 61/020,326, filed Jan.10, 2008; the contents of all of which as are hereby incorporated hereinby reference in their entirety.

BACKGROUND Technical Field

This application relates to LED (light-emitting diode) lamps, and inparticular to an LED lamp to replace standard incandescent lamps.

Incandescent lamps have existed for over a hundred years. They areattractive and aesthetically pleasing for their high Color RenderingIndex (CRI) and warm color temperature. However, low efficiency, shortlife and energy waste have been major drawbacks that forced consumers toswitch to more efficient sources of light, such as the fluorescent lamp.

The incandescent lamp would have become obsolete many decades ago had itnot been for the fact that fluorescent lamps have low CRI, arephysically large, exhibit flicker effect and include hazardous materialssuch as mercury.

Until the late 1980s, LEDs had been primarily used as an indicator lightin electronic equipment. Their high efficiency compared to incandescentmade them very popular. Towards the late 1990s, high intensity LEDsstarted emerging, including the white LED. Today, the advancement in LEDchip design and manufacturing makes it more feasible than ever toreplace the incandescent lamp.

However there remain several challenges that slow the spread of LEDlamps:

1. Low maximum LED junction temperature and heat dissipation.

LEDs generate heat at a rate equal to the product of the voltage dropV_(D) and the drive current I_(D),

$P_{\text{?}} = {{I_{D\text{?}} \times V_{D\text{?}}} = \frac{\Delta \; Q_{\text{?}}}{\Delta \; t_{\text{?}}}}$?indicates text missing or illegible when filed

where P is the power and Q the heat energy produced by the LED. The LEDjunction temperature rise is a function of the difference between heatgenerated and heat dissipated. Heat dissipation is a function of theheat sink surface area, the thermal conductivity of the different mediaand interfaces and the temperature difference between the heat sink andambient temperature. Most LEDs have a maximum junction temperature of125° C. and a few manufacturers advertise up to 180° C. Light outputfrom LEDs is limited by how fast heat can be dissipated away from thedie. The luminous output of LEDs is reduced as the junction temperatureelevates. FIG. 1 is a plot of the luminous output vs. junctiontemperature of a typical LED.

2. Luminous Output and Efficacy.

Luminous Efficacy is the ratio of luminous flux (Lm) to applied power(Watts). Typical values of low power incandescent lamp efficacy are:

Luminous Efficacy LM/W Combustion Candle 0.3 5 W Incandescent 5 40 WIncandescent 12

LED efficacy has improved over the last few years and has exceeded 100Lm/W. Commonly available power LEDs can measure up to 85 Lm/W. However,it should be noted that these measurements are taken at 25° C. junctiontemperature and reduced drive current.

As noted earlier, the luminous output decreases when the die temperatureincreases. Increasing the drive current has an even greater effect onreducing efficacy. As the current increases, the light output increasesin a non-linear fashion, as shown in FIG. 2, but as FIG. 3 shows, thevoltage increases as well.

In other words, if the current I is increased by a factor (1+K, where0<K<1), not only will the luminous output be increased by a factor (k+1,where 0<k<K), but the LED voltage V will also increase by a factor(1+v). The new LED power consumption will become:

P=(1+K)×(V+v)=(1+K)×V+(1+K)×v

where the first term represents the increase in power due to increase incurrent only, and the second term represents the increase in power dueto increase in current and voltage.

Thus, increasing the LED current will increase the LED output at theexpense of reducing its efficacy. The percentage increase in lumens islower than that of the increase in current, which will reduce efficacyat a much higher rate.

3. An LED is a unidirectional light source.

LEDs emit light in a cone that is less than a half space, making itdifficult to be used in a traditional “A” type lamp, as FIG. 4 shows.When mounted on a heat sink and placed in a bulb-like shell, some of thelight will be absorbed by the package and lens material which willreduce the system efficacy, For a successful implementation of the LEDin an ‘A’ type lamp, the LED needs to be elevated to the center of thebulb, but this reduces the thermal dissipation capabilities.

4. Need for power conversion.

LEDs are current driven devices that require a constant current sourcepower supply (FIG. 5). As FIG. 3 indicates, the voltage reflected by anLED is an exponential function of the drive current. An LED cannot bedriven by a voltage source, since the source voltage must match the LEDvoltage. Otherwise, the difference in voltage divided by the totalcircuit resistance will result in a current that would easily exceed themaximum LED rating and cause the device to fail.

A constant current source power supply adds cost and reduces thereliability and efficiency of the LED lamp system. A fly-back powersupply under 5 watts has a typical efficiency of less than 80% whichwill reduce the luminous efficacy of the whole lamp system.

Power supplies occupy valuable real estate in a lamp system, and specialmeasures need to be taken in order to isolate a power supply from theheat generated by the LED.

5. Dimmability.

A dimmer controls the light output by phase controlling the AC inputvoltage. However, a constant current power supply will compensate forany change in input voltage in order to keep the output currentconstant. There are specialty power supplies that permit dimmability.These power supplies are designed to produce an output current that isproportional to the RMS input voltage. Such power supplies are generallymore complex and exhibit lower efficiency.

FIG. 5 is a block diagram of an off-line switch mode power supply. Aswitch mode power supply is required to convert the 120 Vac line voltageto a low DC current (10 mA-350 mA). Power supplies of 5 Watts outputpower or less are almost always fly-back type, and have a typicalefficiency of less than 80%. They are also prone to failure if theyencounter a surge, where a spike of high voltage could damage the MOSFETswitch, especially if a surge suppressor, such as an MOV (metal oxidevaristor), is not incorporated.

Another common method of driving low voltage LEDs is by using animpedance in series with AC line to limit the current and drop theexcess voltage across it. This impedance may be a resistor, a capacitoror an inductor. A resistor is the cheapest and most available, but theenergy E=I²·R·Δt it dissipates is lost and cannot be recovered. Thelosses increase with the increase in the difference in voltage betweenthe source voltage and the LED voltage, as demonstrated in FIG. 6.

${{{Assume}\mspace{14mu} V_{s}} = {166\mspace{14mu} V}},{V = {36\mspace{14mu} V}},{{{and}\mspace{14mu} I} = {20\mspace{14mu} {{mA}.{Then}}}},{R = {\frac{V_{s} - V}{I} = {\frac{166 - 36}{0.02} = {6.5\mspace{20mu} k\; \Omega}}}}$

The power dissipation across the resistor is

P _(R) =I ² ×R=2.6W

The efficiency of the system becomes:

$\frac{P_{OUT}}{P_{I\; N}} = {\frac{I \times V}{\left( {I \times V} \right) + P_{R}} = {\frac{0.02 \times 36}{\left( {0.02 \times 36} \right) + 2.6} = {\frac{0.72}{3.32} = {22\%}}}}$

Obviously this system is not feasible.

Another solution is to replace R by an impedance that does not dissipateenergy, such as an inductor or a capacitor. A capacitor is moreavailable in size and value than an inductor. The only limiting factoris the maximum allowable voltage drop across the capacitor. However,this solution renders the LED non-dimmable and increases the size of thecircuit board due to the large size of the AC capacitor which needs tobe rated to the line voltage plus a margin.

The resistor impedance solution would be feasible if the powerdissipation is reduced, which is accomplished if the voltage difference(Vs−V) is reduced. This is done by increasing the number of LEDs inseries until the total LED voltage drop approaches the source voltage Vswhich will reduce the voltage difference (Vs−V) as well as the value ofR required to limit the current.

For example, assume several LEDs are connected in series to produce atotal load voltage V=136V. The new value for R is:

$R = {\frac{V_{s} - V}{I} = {\frac{166 - 136}{0.02} = {1.5\mspace{14mu} k\; \Omega}}}$

The new power dissipation is

P _(R) =I ² _(LOAD) R=0.6W

The new system efficiency becomes

$\frac{P_{OUT}}{P_{I\; N}} = {\frac{I \times V}{\left( {I \times V} \right) + P_{R}} = {\frac{0.02 \times 136}{\left( {0.02 \times 116} \right) + 0.6} = {\frac{2.72}{3.32} = {82\%}}}}$

Clearly, this is well within the acceptable range for power supplyefficiency, which is accomplished by shifting more of the wasted powerto useful power.

BRIEF SUMMARY

The invention is directed to an LED lamp comprising a base and anelevated light source. The light source is composed of a first pluralityof LEDs connected in series and mounted on one side of a generally flatsubstrate, the substrate being spaced from the base, and a secondplurality of LEDs, connected in series and mounted on an opposite sideof the substrate, with the second plurality of LEDs being locatedgenerally in registration with the first plurality of LEDs. A heat sinkis in the substrate, with each LED of the first and second plurality ofLEDs being mounted proximate the heat sink. A drive circuit is providedfor the LEDs, the drive circuit being located proximate and electricallyconnected to the base.

In accordance with the preferred form of the invention, the base is ascrew-type base. The drive circuit is mounted on a circuit boardextending from the flat substrate, the circuit board extending into thebase.

In one form of the invention, the heat sink comprises at least oneconductive heat island on each side of the substrate, each LED of thefirst plurality of LEDs being proximate a heat island on the one side ofthe substrate, and each LED of the second plurality of LEDs beingproximate a heat island on the opposite side of the substrate. The heatsink also includes at least one conductive heat spreader, each heatisland being connected to the heat spreader. The heat spreader islocated in the substrate, and extends to the base. Preferably, there arefirst and second heat spreaders, with each heat island on one side ofthe substrate being connected to the first heat spreader and each heatisland on the opposite side being connected to the second heat spreader.Each heat spreader is preferably a unitary structure, although the heatspreaders can be a series of conductive elements connected to oneanother.

Preferably, the invention is in the shape of a conventional light bulb.It therefore includes a globe which is connected to the base. The firstand second plurality of LEDs are oriented generally in an arc inside theglobe.

The drive circuit comprises a surge suppressor, a rectifier, a smoothingcapacitor and a resistor, with the first plurality of LEDs and thesecond plurality of LEDs being connected in parallel and their parallelconnection being to the resistor.

In one form of the invention, the substrate is oriented parallel to aline extending from the base. In a second form of the invention, thesubstrate is oriented perpendicular to the line extending from the base.In this form of the invention, the heat sink comprises a plurality ofconductive heat spreader rods extending from proximate the base to thesubstrate.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The invention is described in greater detail in the followingdescription of examples embodying the best mode of the invention, takenin conjunction with the drawing figures, in which:

FIG. 1 is a plot of the luminous output versus junction temperature of atypical LED,

FIG. 2 is a plot of the light output versus current drive of a LED, FIG.3 is a plot of LED voltage versus LED current,

FIG. 4 is a plot of the cone of light emission of an LED,

FIG. 5 is an off-line switch mode power supply for an LED,

FIG. 6 demonstrates how losses increase with the increase in thedifference between voltage between a source voltage and the LED voltage,

FIG. 7 is an elevational illustration of a circuit board according tothe invention,

FIG. 8 illustrates a simple circuit for connecting LEDs in series,

FIG. 9 is a typical circuit used in connection with the presentinvention,

FIG. 10 represents the waveforms for the input alternating currentvoltage, the rectified voltage and the LED current of the circuit ofFIG. 9,

FIG. 11A is an elevational view, similar to FIG. 7, of one form of theinvention,

FIG. 11B is a side elevational illustration of FIG. 11A,

FIG. 11C is the substrate of FIGS. 11A and 11B showing the heatspreader,

FIG. 12A is an elevational illustration of another form of theinvention, FIG. 12B is an elevational view of another form of theinvention,

FIG. 12C is an elevational view of yet another form of the invention,

FIG. 13A is a perspective schematic illustration of another form of theinvention with the LEDs oriented perpendicular to the earlierembodiments of the invention,

FIG. 13B is a perspective view of the form of the invention shown inFIG. 13A, as a completed lamp,

FIG. 14 is an exploded view of the lamp shown in FIG. 13B,

FIG. 14A is a plan view of another form of the invention for fluorescentlamp replacement,

FIG. 14B is a side elevational view thereof,

FIG. 14C is an enlarged partial top plan view of area A of FIG. 14A,

FIG. 14D is a second version of the embodiment of FIG. 14A,

FIG. 14E is a side elevational view thereof,

FIG. 14F is an enlarged partial top plan view of area A of FIG. 14D, and

FIGS. 15A-15 c illustrate a slightly modified version of the inventionshown in FIG. 11, with FIG. 15A showing the base, FIG. 15B showing thecircuitry and light source, and FIG. 15C showing the globe.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

The invention produces an LED based lamp that overcomes theabove-described limitations of the prior art, namely:

-   -   Simple robust power converter    -   High system luminous efficacy    -   Dimmable    -   Efficient 360° light output    -   Efficient thermal management system    -   Direct replacement for any low power incandescent lamp    -   Designed for manufacturability

The invention utilizes multiple low cost surface mount LEDs connected inseries on a surface board thereby increasing the load voltage drop aswell as the useful light output and the system efficiency (FIGS. 7 and8). This may also be accomplished by assembling LED dies directly on theprinted circuit board (Chip On Board) in the same series combination.

An LED emitter can be packaged by combining LED dies in series toproduce a high combined LED voltage at the rated current. Such an LEDseries will draw the same current as a single LED, but will reflect avoltage that is very close to the rectified source voltage. This isdifferent from the Seoul Semiconductor “Acriche” LED where the dies areconnected in antiparallel, thereby eliminating the need for a rectifierand transforming the LED into a high voltage AC LED. Combining LEDs inseries results in a high voltage DC LED, which will require a rectifierwhen operated from an AC source. The advantage is the ability to add asmoothing capacitor to reduce current ripple and attain a steady lightsource with no flicker. The Acriche LED does not allow for a smoothingcapacitor to be installed since the rectification process is internal tothe package.

The assembly of surface-mount devices (SMD) is an automated and low costprocess. It is therefore critical that all components are SMD type. Thisis another reason a high voltage AC capacitor is not feasible since theyare hard to find in SMD.

FIG. 9 is a schematic of a typical circuit according to the invention,designated generally at 10. The invention is described in relation to analternating current source 12 although obviously if direct current isavailable, then a rectifier is unnecessary. The alternating currentsource 12 is supplied through a fuse to a rectifier 16. The rectifier 16rectifies the alternating current to produce a voltage source,illustrated schematically at 18. A series resistor 20, described above,is followed by two parallel combinations of LEDs 22 in series and LEDs24 in series. To increase the reliability of the circuit 10, a surfacemounted MOV (metal oxide varistor) surge suppressor 26 is also included.A smoothing capacitor 28 reduces current ripple and eliminates flicker.

The efficiency may be further improved by adding more LEDs in series,thus increasing the total voltage drop.

In general, let ΔV=Vs−V which is the voltage across the resistor 20. Fora given load current I,

$R = {{\frac{\Delta \; V}{I}\mspace{14mu} {and}\mspace{14mu} P_{R}} = {I \times \Delta \; {V.}}}$

An adverse effect of a low ΔV is poor regulation. Since the LED voltagedrop is not sensitive to current (FIG. 3), a change in the input voltagewill be applied to ΔV only, which will cause the current to change in aproportional manner.

If δV is the change in the source voltage Vs, the same change will beapplied to R, which is now constant. The new current will become:

$I = \frac{{\Delta \; V} + {\delta \; V}}{R}$

where δV may be positive or negative. Let δI represent the change inload current. Then

${{Reg}.} = {\frac{\delta \; I}{I} = {\frac{\frac{\delta \; V}{R}}{\frac{\Delta \; V}{R}} = \frac{\delta \; V}{\Delta \; V}}}$

Regulation will be defined as the percentage change in output:

Regulation is to be made as small as possible in order to minimize thechange in output as the input changes. But a low value for regulationmeans a large value for ΔV, which increases the losses and reduces theefficiency, as described earlier.

${P_{R} = {{I \times \Delta \; V} = \frac{\left( {\Delta \; V} \right)^{2}}{R}}},{{{and}\mspace{14mu} {efficiency}\mspace{14mu} \frac{P_{OUT}}{P_{I\; N}}} = {\frac{I \times V}{\left( {I \times V} \right) + P_{R}}.}}$

One aim of the invention is to specify the largest acceptable regulationfor a given change δV in source voltage Vs. This will define thesmallest ΔV, which will be used to determine R and the efficiency of thesystem.

FIG. 10 represents the waveforms of the input AC voltage, the rectifiedvoltage, and the LED current.

LEDs are most efficient when driven at a relatively low current wherethe losses are the lowest. However, this also means that the total lumenis low. For example, if an LED has an efficiency of 100 Lm/W at 0.03 W,then its output will be 3 lumens. An efficient LED does not necessarilymean a bright LED. On the contrary, the most efficient LED may be so dimthat it will be rendered unusable as a light source for illumination.

Some prior LEDs have been made up of multiple smaller LEDs, mounted onan insulated aluminum substrate, but they are arranged in series andparallel combination which keeps the total LED voltage low, and itscurrent high. Because the LEDs are packed close to one another, it maybe inefficient for all the light to exit, part of which could beabsorbed by adjacent LEDs. Driving LEDs at a high current will furtherreduce efficacy.

In the present invention, the low cost efficient LEDs 22 and 24 arearranged in series, on both layers of a printed circuit board orsubstrate so as to maximize the total lumen output and reduceabsorption. The LEDs are driven at a low current to keep the efficacyhigh. The low lumen output is compensated by increasing the number ofLEDs. Since LED size is miniature and the PCB placement cost of surfacemount components is low, the only penalty is LED cost.

Consider two luminous intensities, a 15 Watt/75 Lm, and a 25 Watt/200 Lmincandescent equivalent LED lamp.

For the 75 Lm system, 36 LEDs are arranged in series, 18 on either sideof the circuit board in identical locations. The system is shown in FIG.7 and is driven according to the schematic in FIG. 9, at an LED currentof 10 mA. The lumen output per LED at that current is 2 lumens, yieldinga total of 75 lumens at a total input power of 1.2 W, and a total systemluminous efficacy of 60 Lm/W.

The high output version has two parallel circuits of 36 LEDs each oneither sides of the PCB, as shown in FIGS. 11A-11C. The LED current foreach series circuit is increased to 30 mA.

Due to the method in which the LEDs are arranged and mounted inside thelamp, more lumens leave the lamp due to less absorption and obstruction.

Even though the large number of LEDs in each circuit will ensure equalcurrent sharing, series resistors 30 are added for each circuit 10 tohelp dissipate the increase in losses due to the higher output, as wellas improve current sharing, The surface mount MOV surge suppressor 26and fuse 14 can also be added to increase reliability.

Even though the previous discussion was limited to two power levels, thesame principle can be applied to achieve a higher power of 40 Wattsequivalent or higher. The total system efficacy can be increased byutilizing more LEDs and reducing the drive current.

The brightness of an LED is limited by the maximum junction temperature.In most cases, the junction temperature is 125° C. Assuming atemperature difference of 10° C. between junction and case, a rule ofthumb is to maintain a case temperature of no more than 95° C. with a15° C. margin. The more heat dissipated from the LED junction, thehigher the attainable light output.

For prior art power LED lamps of 6 Watts or higher, an external heatsink is usually implemented, which places the LED directly on the heatsink, reducing its affectivity and increasing cost.

The present invention offers an alternate method of LED heatdissipation. Rather than dissipating heat from one power LED through anexternal heat sink, multiple low power LEDs 24 and 26 dissipate theirheat through heat spreader copper islands 32 and 34 on top and bottomlayers of a multi-layered PCB board or substrate 36. The islands 32 and34 transfer the heat to two inner layers of copper heat spreaders 38 and40. Each is located very close to the heat islands 32 and 34 on theouter layers. The inner spreaders 38 and 40 conduct heat internally to ascrew base 42 of the lamp, which in turn will dissipate it away throughthe fixture and electrical wiring (not illustrated). Since the screwbase 42 is connected to AC line, it needs to be fully isolated from therest of the circuit 10. The core thickness of the substrate 36 betweenthe outer islands 32 and 34 and the inner heat spreaders 38 and 40should have the minimum thickness that the safety standards will allowto reduce thermal resistance to a minimum and maximize heat transfer.

Since in this invention heat is dissipated through conduction to thescrew base, the lamp can be placed inside a sealed globe 44 (FIG. 12A,etc.) with no air circulation. It will also allow for more light toradiate, since the LEDs are elevated and more visible.

At the bottom of the LED substrate 36, the heat spreaders 38 and 40 arethermally bonded together by printed circuit board vias, which are meansto provide electrical connection between traces on different layers of acircuit board, in order to maximize power dissipation to the screw baseby thermally conducting heat from one layer to another.

The LEDs 22 and 24 are positioned on the substrate 36 in an arrangementof an arc that resembles the filament of an incandescent light bulb,with the intention of maintaining its classic look. The power conversionpart of the system is installed on a circuit board portion of thesubstrate 36 in order to minimize cost and simplify assembly. All thecomponents are surface-mount devices which allows for automation.

The LEDs 22 and 24 are placed in registration on either side of thesubstrate 36 in preferably exactly the same relative location whichgives the impression of transparency. Since no external heat sink isused, the lamp globe 24 can be made entirely of transparent materialwith the LEDs 22 and 24 elevated to maximum lumen efficacy. To betterresemble the incandescent lamp, the LED Correlated Color Temperature(CCT) should be 2800° K, which is close to that of an incandescent lamp,and the Color Rendering Index (CRI) should be typically 95. The effectwill be to create an identical application, effect and look of anincandescent light bulb.

The LEDs are precisely placed on either side of the substrate 36 to makethe substrate look invisible. The effect is for the observer to see onlythe trace of light. The shapes and arrangement of the LEDs may varydepending on the effect required.

FIG. 12A depicts an A19 and FIGS. 12B and 12C depict B10 type lamps.This invention allows the use of this arrangement of LEDs in any lowpower incandescent application, including decorative lamps. The patternin which the LEDs are arranged is not limited to those shown in FIG. 12,and may extend to any arrangement to produce any desired effect.

FIGS. 13A, 13B and 14 are other embodiments of the invention where theheat collectors are solid rods 46 bonded to the heat islands. In thiscase, the lamp will retain more resemblance to the classicalincandescent lamp. The elements are the same as the first form of theinvention, but since the substrate is horizontal, all elements have theidentifier “a”. The power supply circuit 10 is located in the screw base42 of the lamp.

The LEDs 22 and 24 may be incorporated in a plastic polymer shaped as afilament. The LEDs 22 and 24 may be arranged to illuminate the polymerwhich will efficiently conduct light and give the impression ofcontinuous filament glow.

Another embodiment is to mount LED dies directly on the substrate 36 inthe same pattern (Chip on Board), and apply phosphor on all the dies atonce. This will make the group of LED dies glow as one. It can alsoreduce the LED cost since they are not packaged individually.

The choice of resistive impedance R makes it possible to use withconventional Triac dimmers in a manner similar to incandescent lamps.The only limitation is the LED current which must be higher than theTriac Holding current, which is usually the case since the low intensityB10 type lamps are usually arranged in groups of 5 or more inchandeliers.

The LEDs 22 can also be arranged in a linear fashion to replace afluorescent lamp, as shown in FIGS. 14A through 14F. In this form of theinvention, the LEDs 22 are on one side of a PCB board or substrate 36 b,while the circuit 10 is located on the opposite side of the board 36 b.

Just as in the earlier forms of the invention in relation to replacementof an incandescent lamp, the lamp of FIGS. 14A-14F can be completelyenclosed in a tube or fixture (not illustrated), due to the low amountof generated heat that needs to be dissipated. The LED correlated colortemperature (COT) can be anywhere between 3,000° K to 5,000° K forreplicating and replacing bulbs in current fluorescent light systems.

The invention consists of 3 main parts (FIG. 15), screw base 42, LEDcircuit 10, and lamp globe 44. The LED-bearing substrate 36 is installedin the screw base 42 by first soldering the middle terminal, then bybonding the plated sides to the barrel of the screw base 42.

This will ensure electrical contact as well as provide a thermal passageto conduct the heat generated by LEDs 22 and 24 to the screw base 42 andthe electrical wiring (not illustrated) which will act as an extendedheat sink.

Various changes can be made to the invention without departing from thespirit thereof or scope of the following claims.

What is claimed:
 1. An LED lamp comprising a. a base, b. an elevatedlight source, comprising i. a first plurality of LEDs connected inseries and mounted on one side of a generally flat substrate, saidsubstrate being spaced from said base, and ii. a second plurality ofLEDs, equal in number to said first plurality of LEDs, connected inseries and mounted on an opposite side of said generally flat substrate,said second plurality of LEDs being located on said opposite side ofsaid generally flat substrate generally in alignment with said firstplurality of LEDs, c a heat sink in said substrate, each LED of saidfirst and second plurality of LEDs being mounted proximate said heatsink, and d a drive circuit for said LEDs, said drive circuit beinglocated proximate and electrically connected to said base.
 2. The LEDlamp according to claim 1, in which said base is a screw-type base. 3.The LED lamp according to claim 1, in which said drive circuit ismounted on a circuit board extending from said flat substrate, saidcircuit board extending into said base.
 4. The LED lamp according toclaim 1, in which said heat sink comprises at least one conductive heatisland on each side of said substrate, each LED of said first pluralityof LEDs being proximate a heat island on said one side, and each LED ofsaid second plurality of LEDs being proximate a heat island on saidopposite side.
 5. The LED lamp according to claim 4, in which said heatsink includes at least one conductive heat spreader, each heat islandbeing connected to said heat spreader.
 6. The LED lamp according toclaim 5, in which said heat spreader is located in said substrate, saidheat spreader extending to said base.
 7. The LED lamp according to claim5, including first and second heat spreaders, each heat island on saidone side of said substrate being connected to said first heat spreaderand each heat island on said opposite side being connected to saidsecond heat spreader.
 8. The LED lamp according to claim 7, in whichsaid heat spreaders are unitary.
 9. The LED lamp according to claim 1,including a globe connected to said base.
 10. The LED lamp according toclaim 1, in which said first and second plurality of LEDs are orientedgenerally in an arc.
 11. The LED lamp according to claim 1, in whichsaid drive circuit comprises a surge suppressor, a rectifier, asmoothing capacitor and resistor, said first plurality of LEDs and saidsecond plurality of LEDs being connected in parallel to said resistor.12. The LED lamp according to claim 1, in which said substrate isoriented parallel to a line extending from said base.
 13. The LED lampaccording to claim 1, in which said substrate is oriented perpendicularto a line extending from said base.
 14. The LED lamp according to claim13, in which said heat sink comprises a plurality of conductive heatspreader rods extending from proximate said base to said substrate. 15.The LED lamp according to claim 14, in which said heat sink includes atleast one conductive heat island on each side of said substrate, eachLED of said first plurality of LEDs being proximate a heat island onsaid one side, and each LED of said second plurality of LEDs beingproximate a heat island on said opposite side.
 16. An LED lampcomprising: a base, an elevated light source, comprising: a first set ofLEDs connected in series and mounted on one side of a generally flatsubstrate, said substrate being spaced from said base, and a second setof LEDs, equal in number to said first plurality of LEDs, connected inseries and mounted on an opposite side of said generally flat substrate,said second plurality of LEDs being located on said opposite side ofsaid generally flat substrate generally in alignment with said firstplurality of LEDs, and a set of electrically isolated heat sinks definedin a first portion of said substrate, each LED of said first and secondsets of LEDs being mounted proximate at least one electrically isolatedheat sink of said set of electrically isolated heat sinks.
 17. The LEDlamp according to claim 16, wherein said first portion of said substratecomprises at least one conductive heat island on each side of saidsubstrate, each LED of said first set of LEDs being proximate a heatisland on said one side, and each LED of said second set of LEDs beingproximate a heat island on said opposite side.
 18. The LED lampaccording to claim 16, wherein: said LED lamp further comprises a drivecircuit for said LEDs, said drive circuit is located proximate andelectrically connected to said base, and each LED of said first andsecond sets of LEDs is further mounted proximate a second portion ofsaid substrate so as to provide electrical connection between said drivecircuit and each LED.
 19. The LED lamp according to claim 18, in whichsaid drive circuit comprises a surge suppressor, a rectifier, asmoothing capacitor and resistor, said first plurality of LEDs and saidsecond plurality of LEDs being connected in parallel to said resistor.20. The LED lamp according to claim 16, wherein: said base is orientedabout a central axis extending there-through; and said substrate extendsalong and parallel to said central axis.